Grease composition for constant velocity joints

ABSTRACT

A grease composition for constant velocity joints, having a base oil and a urea-based thickener, which grease additionally contains, (A) molybdenum sulphide dialkyldithiocarbamate and (B) 5,5-dithiobis (1,3,4-thiadiazole-2-thiol); a method of lubricating a constant velocity joint including packing it with grease and a constant velocity joint packed with said grease.

FIELD OF THE INVENTION

The present invention relates to a grease composition for constantvelocity joints, a method of lubricating a constant velocity joint andto a constant velocity joint packed with a grease. In particular, thepresent invention relates to a grease composition which can be used forautomobile drive shafts, propeller shafts and industrial machineryjoints.

BACKGROUND OF THE INVENTION

Recent progress in mechanical technology has seen a growing demand forthe reduction in size and weight of machines, the enhancement of machineprecision, the prolongation of machine life and so forth.

Constant velocity joints are special types of universal couplings whichcan transmit drive from the final reduction gear to a road wheel axle atconstant rotation velocity.

As the constant velocity joints used in automobiles and industrialmachines are used at high speeds and under high surface pressureconditions, much better performance is demanded of the grease used tolubricate these joints. This situation will be described in more detailbelow with reference to constant velocity joints (herein belowabbreviated to CVJ) for automobiles.

With the promotion of front wheel drive cars and four wheel drive carsand the like, there has been a marked increase in the use of CVJ in theautomobile industry. Cars now have higher output and are smaller andlighter, which imposes severe demands on CVJ durability.

The grease used for CVJ lubrication is also subjected to the demands forbetter joint durability and lifetime (damage resistance, for example,flaking resistance and seizing resistance).

In response to these demands, sulphur-phosphorus-based extreme-pressureagents comprising sulphurated fat/oil and/or olefin sulphide combinedwith zinc dithiophosphate, and lithium grease comprising lead-basedadditives and molybdenum disulphide and the like have mainly been usedcommercially. In recent years, urea grease, which has excellent heatresistance, has been used more than lithium grease.

Examples of prior art techniques which involve the use of a molybdenumsulphide dialkyldithiocarbamate include Japanese Examined PatentApplication No. H4-34590 and Japanese Unexamined Patent Application Nos.H6-57283, H6-330072 and H10-273692.

Japanese Examined Patent Publication No. H4-34590 discloses a systemcomprising:—(A) molybdenum sulphide dialkyldithiocarbamate; and (B) atleast one sulphur-phosphorus-based extreme pressure additive chosen fromthe group consisting of sulphurated fat/oil, olefin sulphide, tricresylphosphate, trialkylthiophosphate and zinc dialkyldithiophosphate,compounded into urea grease. However, such systems cannot always be saidto be satisfactory under the current severe CVJ working conditions.

Japanese Unexamined Patent Application No. H6-57283 discloses a systemcomprising molybdenum sulphide dialkyldithiocarbamate, molybdenumdisulphide and lead sulphide dialkyldithiocarbamate, compounded intourea grease. However, as this system contains a lead-based additive, itis undesirable in view of increasing concerns over environmentalprotection.

Japanese Unexamined Patent Application No. H6-330072 discloses addingboth (A) molybdenum sulphide dialkyldithiocarbamate and (C)triphenylphosphorothionate to urea grease, but these systems do notsimultaneously yield satisfactory damage resistance and abrasionresistance.

T. Sakurai's “Sekiyu Seihin Tenkazai” [Petroleum Product Additives] (p.262 and thereafter) introduces thiadiazole compounds as lubricant oiladditives, and Table 3 on p. 266 suggests that the addition ofthiadiazole-based compounds results in excellent sulphuration corrosionprevention with respect to copper and silver. Moreover, JapaneseExamined Patent publication No. H4-32880 discloses improved loadresistance and extreme pressure properties without corrosion ordiscoloration of the metal as a result of adding5,5′-dithiobis(1,3,4-thiadiazole-2-thiol) to lubricating grease, but nomention is made of the problem of balancing damage resistance andabrasion resistance.

Japanese Unexamined Patent Application No. H11-131086 discloses the useof a thiadiazole-based compound as an additive in lubricating greaseobtained using a calcium sulphonate complex-based thickening agent, butthe thiadiazole-based compound is used here to deactivate metals.

Japanese Unexamined Patent Application No. H10-273692 discloses a greasecomposition for constant velocity joints comprising diurea as thickener,wherein molybdenum disulphide, phosphorus-free sulphur-based extremepressure additive and sulphur-nitrogen-based extreme pressure additiveare used in combination with (A) molybdenum sulphidedialkyldithiocarbamate. However, it is not clear which specificcompounds can be used as the sulphur-nitrogen-based extreme-pressureagent, as “Vanlube 601” (trademark), manufactured by R. T. Vanderbilt,is merely disclosed in the working examples, and said trade name merelyconfirms that “Vanlube 601” is a heterocyclic sulphur-nitrogen compound.Moreover, according to this technique, the combined use of molybdenumdisulphide and phosphorus-free sulphur-based extreme pressure additiveis indispensable.

EP-A-0633 304 discloses a urea grease composition comprising a ureagrease and, incorporated therein as additives, a sulfurized molybdenumdialkyldithiocarbamate represented by formula (A):-(R₁R₂N—CS—S)₂—Mo₂O_(m)S_(n)wherein R₁, and R₂ each independently represent an alkyl group havingfrom 1 to 24 carbon atoms, m+n=4, m is 0 to 3, and n is 4 to 1, andtriphenylphosphorothionate (B).

There is a demand for both satisfactory damage resistance andsatisfactory abrasion resistance in the field of lubricating greasecompositions for constant velocity joints. There are many greases whichhave good abrasion resistance but poor damage resistance. There isconsiderable demand for the discovery of a grease composition forconstant velocity joints which provides improvement in both of thesephysical properties.

It has now been found possible to formulate greases for constantvelocity joints containing 5,5′-dithiobis(1,3,4-thiadiazole-2-thiol),having advantageous properties with regard to damage resistance andabrasion resistance.

SUMMARY OF THE INVENTION

The present invention provides a grease composition for constantvelocity joints comprising a base oil and a urea-based thickener, whichgrease additionally contains, (A) molybdenum sulphidedialkyldithiocarbamate; and (B)5,5′-dithiobis(1,3,4-thiadiazole-2-thiol).

DETAILED DESCRIPTION OF THE INVENTION

In a preferred embodiment, the grease composition of the presentinvention further contains, (C) triphenylphosphorothionate.

The molybdenum sulphide dialkyldithiocarbamate (A) may conveniently be acompound represented by general formula (1) below:-(R¹R²N—CS—S)₂—Mo₂O_(m)S_(n)  (1)wherein R¹ and R² are groups independently chosen from the groupconsisting of alkyl groups of from 1 to 24 carbon atoms, m+n=4, m isfrom 0 to 3 and n is from 1 to 4.

Preferred alkyl groups are those having from 1 to 18 carbon atoms, morepreferably from 1 to 12 carbon atoms, even more preferably from 1 to 6carbon atoms and most preferably from 1 to 4 carbon atoms. Said alkylgroups maybe linear or branched.

Specific examples of molybdenum sulphide dialkyldithiocarbamate (A) thatmay be conveniently used in the present invention include one or more ofmolybdenum sulphide diethyldithiocarbamate, molybdenum sulphidedibutyldithiocarbamate, molybdenum sulphide diisobutyldithiocarbamate,molybdenum sulphide di(2-ethylhexyl)dithiocarbamate, molybdenum sulphidediamyldithiocarbamate, molybdenum sulphide diisoamyldithiocarbamate,molybdenum sulphide dilauryldithiocarbamate, molybdenum sulphidedistearyldithiocarbamate, molybdenum sulphiden-butyl-2-ethylhexyldithiocarbamate and molybdenum sulphide2-ethylhexylstearyldithiocarbamate.

5,5′-dithiobis(1,3,4-thiadiazole-2-thiol) (B) may be represented byformula (2) below:-

Preferred compositions according to the invention have one or more ofthe following features:

-   (i) from about 0.5% to about 10% by weight of A;-   (ii) from about 0.5% to about 5% by weight of A;-   (iii) at least about 2% by weight of A;-   (iv) up to about 3% by weight of A;-   (v) from about 0.1% to about 10% by weight of B;-   (vi) from about 0.1% to about 5% by weight of B;-   (vii) at least about 0.5% by weight of B, and-   (viii) up to about 2% by weight of B, with respect to the total    weight of the grease composition.

Particularly preferred compositions according to the invention are thosehaving features (i) and (v); those having features (i) and (vi); thosehaving features (i) and (vii); those having features (i) and (viii);those having features (i), (vii) and (viii); those having features (ii)and (v); those having features (ii) and (vi); those having features (ii)and (vii); those having features (ii) and (viii); those having features(ii), (vii) and (viii); those having features (iii) and (v); thosehaving features (iii) and (vi); those having features (iii) and (vii);those having features (iii) and (viii); those having features (iii),(vii) and (viii); those having features (iv) and (v); those havingfeatures (iv) and (vi); those having features (iv) and (vii); thosehaving features (iv) and (viii); those having features (iv), (vii) and(viii); those having features (iii), (iv) and (v); those having features(iii), (iv) and (vi); those having features (iii), (iv) and (vii); thosehaving features (iii), (iv) and (viii); and those having features (iii),(iv), (vii) and (viii).

If less than about 0.5% by weight of A is used, a reduced effect on theCVJ damage resistance is achieved, whereas there is no incentive to usemore than about 10% by weight of A, as above this concentration limitedor no further improvement can be expected.

If less than about 0.1% by weight of B is used, a reduced effect on theCVJ damage resistance is achieved, whereas there is no incentive to usemore than about 10% by weight of B, as above this concentration limitedor no further improvement can be expected.

The triphenylphosphorothionate (C) is a compound represented by formula(3) below:-(C₆H₅—O)₃—P═S  (3)

When triphenyiphosphorothionate (C) is added, it is preferablyincorporated in a concentration of up to about 10% by weight, e.g., fromabout 0.1% to about 10% by weight, more preferably from about 0.1% toabout 5% by weight, with respect to the total weight of the greasecomposition.

If less than about 0.1% by weight of C is added, a reduced effect on theabrasion resistance is achieved, whereas there is no incentive to usemore than about 10% by weight of C, as above this concentration limitedor no further improvement can be expected.

Any urea-based thickener can be used as the urea compound used for thethickener, and there are no particular limitations on the type thereof.For example, diurca, triurea and/or tetraurea may be conveniently used.Mineral oil and/or synthetic oil is used as the base oil. In a preferredembodiment of the present invention, from about 2% to about 35% byweight of urea-based thickener is used with respect to the total weightof the grease composition.

It is also possible to add various additives such as antioxidants, rustpreventers and extreme-pressure agents to the grease composition of thepresent invention.

Preferred lubricating grease compositions for constant velocity jointsaccording to the invention specifically described herein haveconsiderably improved flaking resistance and seizing resistance (damageresistance) and also have excellent abrasion resistance andtemperature-control properties.

The present invention will now be described with reference to thefollowing examples, which are not intended to limit the scope of thepresent invention in any way.

EXAMPLES

Preparation of Grease Compositions

Additives were added to base grease according to the formulations shownin Tables 1 to 3, and the resulting systems were treated using a3-roller mill to yield grease for the Working Examples and ComparativeExamples. It should be noted that purified mineral oil having akinematic viscosity of 15 mm²/s at 100° C. was used as the base oil.

I Diurea Grease

1 mol of diphenylmethane-4,4′-diisocyanate and 2 mol of octylamine werereacted in base oil, and the resulting urea compound was uniformlydispersed to yield base grease. The urea compound content was set atabout 10% by weight.

II Tetraurea Grease

2 mol of diphenylmethane-4,4′-diisocyanate, 2 mol of octylamine and 1mol of ethylene diamine were reacted in base oil and the resulting ureacompound was dispersed uniformly to yield base grease. The urea compoundcontent was set at about 15% by weight.

The thickness, abrasion resistance, joint damage and joint durabilityshown in the accompanying tables were appraised according to thefollowing test methods.

-   (1) Thickness was appraised according to JIS K2220 5.3-   (2) Abrasion resistance was appraised according to ASTM D2266.-   (3) Joint damage test

Each sample was introduced into a commercial CVJ and the system wasoperated under the following conditions, then the presence or absence ofthe fine damage that is a sign of flaking inside the joint wasappraised, and the maximum temperature of the joint during the operationwas also appraised.

-   CVJ type: Barfield joint-   rpm: 1500 rpm-   Joint angle: 8°-   Torque: 300 N.m-   Time: 1 hour-   Appraisal: (O) no damage; x damage; Δ slight damage-   (4) Joint durability test

Each sample was introduced into a commercial CVJ and the system wasoperated under the following conditions, then the presence or absence offlaking or seizure of the ball in the joint or of the inner race, outerrace or cage was appraised.

-   CVJ type: Barfield joint-   rpm: 1500 rpm-   Joint angle: 8°-   Torque: 300 N.m-   Time: 150 hours-   Appraisal: (O) no damage; Δ slight flaking; x flaking (continued use    impossible)

TABLE 1 Working Working Working Example Example Example 1 2 3 Basegrease Diurea grease 95.0 95.0 — (% wt) Tetraurea grease — — 95.0Additives A-1 *1 3.0 2.0 — (% wt) A-2 *2 — — 2.0 B *3 2.0 0.5 0.5 C *4 —1.0 1.0 Test results Thickness 60 W 320 316 318 Abrasion 0.47 0.40 0.39resistance (mm) Joint damage (O) (O) (O) test Joint 128 101 108temperature (° C.) Joint durability (O) (O) — test

TABLE 2 Compara- Compara- Compara- tive tive tive Example ExampleExample 1 2 3 Base grease Diurea grease 92.0 96.0 98.0 (% wt) Tetraureagrease — — — Additives A-1 *1 3.0 3.0 — (% wt) A-2 *2 — — — B *3 — — 2.0C *4 1.0 1.0 2,5-bis (tert- 4.0 — — octyldithio)- 1,3,4-thiadiazole Zincdialkyl — — — dithiophosphate Molybdenum — — — disulphide Test Thickness60 W 312 326 321 results Abrasion 0.45 0.39 0.55 resistance (mm) Jointdamage test Δ x x Joint temperature 120 107 154 (° C.) Joint durabilityΔ x — test

TABLE 3 Compara- Compara- Compara- tive tive tive Example ExampleExample 4 5 6 Base grease Diurea grease 96.0 96.0 92.0 (% wt) Tetraureagrease — — — Additives A-1 *1 — 3.0 3.0 (% wt) A-2 *2 — — — B *3 1.0 — —C *4 1.0 — — 2,5-bis (tert- 2.0 — — octyldithio)- 1,3,4-thiadiazole Zincdialkyl — 1.0 — dithiophosphate Molybdenum — — 5.0 disulphide TestThickness 60 W 322 318 316 results Abrasion 0.48 0.41 0.65 resistance(mm) Joint damage test x x x Joint temperature 106 108 118 (° C.) Jointdurability — x — test *1 A-1 is a molybdenum sulphidedialkyldithiocarbamate mixture where the alkyl groups have 4 carbonatoms and n is 2 and 3. *2 A-2 is a molybdenum sulphidedialkyldithiocarbamate compound where the alkyl groups have 4 carbonatoms and n is 4. *3 B is the thiadiazole compound5,5′-dithiobis(1,3,4-thiadiazole-2-thiol). *4 C istriphenylphosphorothionate.

1. A grease composition for constant velocity joints, comprising a base oil and a urea-based thickener, which grease additionally contains, (A) molybdenum sulphide dialkyldithiocarbamate and (B) 5,5′-dithiobis(1,3,4-thiadiazole-2-thiol).
 2. The grease composition according to claim 1, containing from about 0.5% to about 10% by weight of (A) molybdenum sulphide dialkyldithiocarbamate and from 0.1% to 10% by weight of (B) 5,5′-dithiobis(1,3,4-thiadiazole-2-thiol), with respect to the total weight of grease composition.
 3. The grease composition according to claim 1, wherein said grease contains from about 0.5% to about 5% by weight of (A) molybdenum sulphide dialkyldithiocarbamate and 0.1% to about 5% by weight of (B) 5,5′-dithiobis(1,3,4-thiadizole-2-thiol), with respect to the total weight of grease composition.
 4. The grease composition according to claim 1, wherein said grease contains from about 2% to about 35% by weight of urea-based thickener, with respect to the total weight of the grease composition.
 5. The grease composition according to claim 1, wherein (A) molybdenum sulphide dialkyldithiocarbamate is selected from one or more of molybdenum sulphide diethyldithiocarbamate, molybdenum sulphide dibutyldithiocarbamate, molybdenum sulphide diisobutyldithiocarbamate, molybdenum sulphide di(2-ethylhexyl)dithiocarbamate, molybdenum sulphide diamyldithiocarbamate, molybdenum sulphide diisoamyldithiocarbamate, molybdenum sulphide dilauryldithiocarbamate, molybdenum sulphide distearyldithiocarbamate, molybdenum sulphide n-butyl-2-ethylhexyldithiocarbamate and molybdenum sulphide 2-ethylhexylstearyldithiocarbamate.
 6. The grease composition according to claim 1, which further contains, (C) triphenylphosphorothionate.
 7. The grease composition for according to claim 6, containing from about 0.1% to about 10% by weight of (C) triphenylphosphorothionate, with respect to the total weight of grease composition.
 8. The grease composition according to claim 6, wherein said grease contains from about 0.1% to about 5% by weight of (C) triphenylphosphorothionate, with respect to the total weight of grease composition.
 9. A method of lubricating a constant velocity joint comprising packing it with a grease according to claim
 1. 10. A constant velocity joint packed with a grease according to claim
 1. 